A variety of different technologies are used in modern internal combustion engines to optimize efficiency and manage emissions. In many engines it is desirable to limit production or output of particulate matter, oxides of nitrogen or “NOx,” and other materials such as unburned hydrocarbons, and carbon monoxide. Engine operating strategies for limiting certain emissions, including variable valve actuation strategies, post injections, pre-injections, exhaust gas recirculation or “EGR,” exhaust back pressure control strategies, and a host of others have been proposed over the years, with varying degrees of success. It is also well-known to treat exhaust directly, by way of catalyst-based reduction of certain exhaust constituents, particulate traps, and still others. Despite many advances across a range of technologies, engineers continue to search for improved ways to operate engines and ancillary engine systems, and new or further refined component designs, with the goal of optimizing engine emissions without sacrificing performance, efficiency or other desirable factors.
In recent years, significant engineering effort has gone into the development of improved fuel injector designs and operating techniques, notably for compression ignition diesel engines. It has been observed that relatively high fuel pressure can promote fuel atomization, which in turn tends to be associated with more complete burning of injected fuel and reduced production of particulate matter. Other techniques seek to strictly control start of injection and end of injection so as to provide a desirable, typically square, injection rate shape that provides desirable combustion characteristics.
One particular fuel injector design is known from U.S. Pat. No. 6,601,566 to Gillis et al., including directly controlled dual concentric checks in a fuel injector for a dual fuel engine. In the dual fuel environment of Gillis et al. two separate fuel injection checks can be packaged in a relatively modest space, and enabling use of two distinct quantities of liquid fuel to various ends, including operating the engine relatively more efficiently and more completely burning the fuel to produce lowered emissions.